Charge-Transfer-Regulated Selective Solar Fuel Production in Aqueous Medium by a Tetrathiafulvalene-Based Redox-Active Metal–Organic Framework

Developing a suitable photocatalyst for artificial photosynthesis is a challenging and highly relevant assignment in contemporary research related to energy and environment. Here, we report photocatalytic CO 2 reduction in aqueous medium under visible light by a conducting Zn (II) MOF, Zn-TTF-MOF synthesized by using a redox active tetrathiafulvalenetetracarboxylate linker. Zn-TTF-MOF displays an intramolecular charge-transfer (intra-CT) band from TTF to the Zn(II)-coordinated benzenecarboxylate unit in visible light with a optical band gap of 1.83 eV. Under visible light, Zn-TTF-MOF enables the production of 784.4 μmol g –1 CO in 10 h from CO 2 in water with a selectivity of ∼94% without additional sacrificial electron donor, cocatalyst, or exterior photosensitizer. The low exciton binding energy results in efficient charge separation in the MOF, as realized by the transient photocurrent and electrochemical impedance spectroscopy measurement under light irradiation. Finally, a plausible CO 2 reduction mechanism is derived based on an in situ diffuse-reflectance infrared Fourier transform study (DRIFTS) followed by DFT calculations.